Reading fired primers

'Boo

'Boo

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Here is a pretty good visual look at some primers during load development.

There are 3 rounds per powder charge increasing from left to right with a 1 grain powder increase at each step. The centre rows shows the progressive flattening of the primer cups the best.

July_20_2010_2.jpg
 
heavyBullet said:
LOL ok now I do not feel so dumb, I was thinking the same thing. Since I only started reloading last fall, I was really hoping to learn something here, but they all look the same to me also.
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Look at the rounded edge of the primer. the first row is still rounded and shiny.
As the charge increases,that rounded edge gets squarer and the primer looks bigger in the pocket. Hard to tell the first 2 rows apart but last row primers are visibly flatter.
 
desperation said:
So are any of these dangerously "over pressure"? I susspect not as you kept firing other loads but how much farther ight you go?
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It's hard to say for sure, going with just primers. Flat primers in conjunction with another pressure sign, such as hard extraction or an ejector recess marking from brass flow would be a definite sign of excess pressure.
 
tjhaile said:
It's hard to say for sure, going with just primers. Flat primers in conjunction with another pressure sign, such as hard extraction or an ejector recess marking from brass flow would be a definite sign of excess pressure.
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As noted by tjhaile primer flattening is only one indicator that a reloader can use to estimate chamber pressure. Brass flow, case head growth, primer pocket expansion, and velocity must also be examined carefully to see if excess pressure is being generated.

In this particular instance the loads on the far right will be the maximum I will load for that particular rifle. The condition of the primer and the velocity obtained - about what the manual indicated using a longer barrel- tell me to stop at that point.
 
Nice round edges on the primer (on left)...not flat and flush up against the pocket like the ones on the right.

Cratering pin strikes are misleading especially in newer Model 700's where the hole is bigger..inviting brass to flow inwards.
 
OEM said:
Cool. So which one is optimum?
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That'll depend on a given gun.

For example:

My Savage .308 (Model 10 FCP, HS Precision) likes 'em to look like the middle row, second from the right. So just on the edge of flattened. Any more, and my group size actually increases.

I have a .25-06 I'm keeping for a friend, which she implores me to shoot because her Dad would want it that way (her late Father custom-made the stock, and I keep it in my safe since it's more secure than her arrangement). That one likes 'em as flat as the right-most column, so I have to read brass flow for overpressure rather than looking for just the primer shape.

Bear in mind that certain primers have different thicknesses too - a Federal 210M is going to react differently than a CCI 34, for example. So, I've had times where I saw extractor flow actually develop BEFORE I saw a full-flat primer... in which case it's time to back it off for sure.

-M
 
'Boo

Good post. Lots of guys have a hard time seeing the differences in fired primers. I usually stop when my primers get to look like your middle row (3rd powder charge in your progression), but you'll likely be fine with the last row as you indicated.
 
Doc M said:
That'll depend on a given gun.

For example:

My Savage .308 (Model 10 FCP, HS Precision) likes 'em to look like the middle row, second from the right. So just on the edge of flattened. Any more, and my group size actually increases.

I have a .25-06 I'm keeping for a friend, which she implores me to shoot because her Dad would want it that way (her late Father custom-made the stock, and I keep it in my safe since it's more secure than her arrangement). That one likes 'em as flat as the right-most column, so I have to read brass flow for overpressure rather than looking for just the primer shape.

Bear in mind that certain primers have different thicknesses too - a Federal 210M is going to react differently than a CCI 34, for example. So, I've had times where I saw extractor flow actually develop BEFORE I saw a full-flat primer... in which case it's time to back it off for sure.-M
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So the ultimate goal is to load it as hot as possible, for the best accuracy? But what about when it appears to be less accurate when its hotter, and yet, the primer face still looks like #01 in the pix?
 
OEM said:
So the ultimate goal is to load it as hot as possible, for the best accuracy? But what about when it appears to be less accurate when its hotter, and yet, the primer face still looks like #01 in the pix?
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No, the ultimate goal isn't necessarily to load it as hot as possible.

Like I said, my Savage likes it backed off a bit. Down from 2,800 or so fps to 2,650 fps means group sizes shrink.

But, if one is shooting at long distances, HOT can sometimes be the order of the day... for example, if one wants to keep the drops within scope-adjustment on some models (e.g. without a 20MOA rail, if one is cheaping out :p ), or if one wants a real barnburner so it's less sensitive to crosswind.

If it's less accurate when you sizzle it up, then don't sizzle it up - nobody ever got hurt from a moderately-loaded cartridge... and it didn't do the gun any harm, either. :)

If you're still looking like column #1, and you've got an accurate load which just gets worse when you juice it up any farther, then leave it where it is - and be thankful that your rig shoots best at the lower end of the pressure/velocity spectrum, because your barrel will last incrementally longer! :)

Where this becomes a concern (for me, anyway) is when I'm loading the long-range barnburners, and I've got 'em riiiiiiight to the max. And it's 15ºC outside. And I know that I'll end up shooting them at 30ºC at some point. Now, if it's already 'maxed' at 15ºC, and you shoot it at 30ºC, you're in "Danger, Will Robinson" territory... or at least potentially, anyway.

So, if I cook up a batch that's maxed at 30ºC, based on pressure signs, then I know it'll be good at 15ºC or anywhere below that. But I can't do the reverse - max 'em at 15ºC and let 'em eat at 30ºC - and be guaranteed of safety.

Finally, even if it's cold outside, if you've left your ammo in the sun (the 'car greenhouse' as I like to think of it), it'll often shoot at WAY higher pressure.

A directly observable bit of this happened to me shooting low-pressure .300 Fireball subsonics in my AR15 about a month ago. Had a few on the bench, and a few more in the car - in the shining sun. The load was 1020 fps (just subsonic - 1150 fps is a rough guideline for the speed of sound, for most Canadian summer temperatures) when 'cool' on the bench under cover, but when taken from the car the same (identical!) batch was shooting 1260 and had a sonic crack.

So, in my experience, the pressure signs give you a good idea of exactly where to stop - and then, backing off from there, I know I've got a good load that has some safety margin which is dependent on temperature.

-M
 
Doc M said:
No, the ultimate goal isn't necessarily to load it as hot as possible.
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Exactly!

In this particular instance the accuracy of the 3rd batch was the best of the group. (Even though we all should know a single good group doesn't mean too much as shots will sometimes pull into a group as easily as pulling out. ;) LoL )

The difference in velocity between the 3rd string and the 5th was ~ 100fps which means less than a 2" difference in drop at 300 yards - using a 200 yard zero - with this particular cartridge.

The ambient temperature issue mentioned by Doc M also shows up in these fired cases. The day I shot these it was ~22 C - warm but not hot. The strings were shot using 3 fast shots as may be seen in a real-life scenario. ;) The cases were returned to the box with the first shot placed at the top of the row, the second in the middle and the last at the bottom. As the chamber heated up the pressure seemed to build a bit on the successive shots even though the powder charge was the same. As can be seen on the pictures not only did the flattening increase with powder charge increases it also appears to have increased as the chamber heated up.

BTW, The powder I was using - Winchester 760 - while very accurate in most cartridge is known for being fairly susceptible to temperature induced pressure excursions. The primers are CCI BR2 which are fairly mild as large rifle primers go.
 
'Boo said:
The ambient temperature issue mentioned by Doc M also shows up in these fired cases. The day I shot these it was ~22 C - warm but not hot. The strings were shot using 3 fast shots as may be seen in a real-life scenario. ;) The cases were returned to the box with the first shot placed at the top of the row, the second in the middle and the last at the bottom. As the chamber heated up the pressure seemed to build a bit on the successive shots even though the powder charge was the same. As can be seen on the pictures not only did the flattening increase with powder charge increases it also appears to have increased as the chamber heated up.
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This is something I knew I was going to forget to mention! :)

He's right, in that as your rifle heats up - and if you keep a round chambered for some time, say while you aim at a distant target - you can increase pressure and velocity too. So keep that in mind if you're a "take your time" shooter and you're shooting loads that are maxed when they're cold. What're they going to be like when they heat up to 50ºC or more in a well-shot and HOT chamber?

It's definitely important to keep your eye on the "pressure gauge" that the primer represents.

-M
 
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